Replaces and virtual packages

[Christoph Pfisterer <cp@chrisp.de>]

Hi!

While trying to set up a group of packages to be mutually-exclusive, 
I've come across what I think is a bug in dpkg. First, some 
background: I'm using dpkg 1.9.17 on Mac OS X (a.k.a. Darwin) in the 
Fink project (http://fink.sourceforge.net). Fink has its own source 
package format, but uses dpkg to install binary .deb packages (and 
dpkg-deb to create them). I can provide the complete set of patches 
used as well as example .deb packages if requested.

The Debian Policy Manual (version 3.5.6.0 from 2001-07-24) mentions 
in section 7.5.2 that alternative and mutually-exclusive packages can 
be set up using a virtual package name and gives the following 
example:

  Provides: mail-transport-agent
  Conflicts: mail-transport-agent
  Replaces: mail-transport-agent

Unfortunately, I can't get this to work with dpkg 1.9.17. To isolate 
the problem, I made two packages, test-a and test-b, that both 
contain these declarations:

  Provides: test-c
  Conflicts: test-c
  Replaces: test-c

When test-a is installed, the expectation is that I can run 'dpkg -i 
test-b_....deb' and it will remove test-a in favor of test-b. (This 
actually works when only real package names are used for Conflicts 
and Replaces.) However, with the above I get this:

[...]
dpkg: regarding .../test-b_1.0-1_darwin-powerpc.deb containing test-b:
 test-a conflicts with test-c
  test-b provides test-c and is to be installed.
dpkg: error processing 
/sw/fink/dists/local/main/binary-darwin-powerpc/test-b_1.0-1_darwin-powerpc.deb 
(--install):
 conflicting packages - not installing test-b
[...]

So somehow dpkg doesn't evaluate the Replaces field correctly in this 
case. Is this a bug? Or am I missing something important and it's 
actually a feature? Could it be related to something obscure, such as 
the ordering of the fields in the control file?

Any help is appreciated.

-chrisp

--
chrisp a.k.a. Christoph Pfisterer   "Any sufficiently advanced
cp@chrisp.de - http://chrisp.de      bug is indistinguishable
PGP key & geek code available        from a feature."